1. Field of the Invention
This invention pertains to loudspeakers. More particularly, it pertains to networks for connecting sources of audio frequency electrical signals to loudspeaker drivers in a manner which compensates for certain undesirable characteristics of the drivers.
2. Description of the Prior Art
Piezoceramic high-frequency drivers for loudspeakers typically exhibit an input impedance which is approximately equivalent to the parallel combination of a capacitor and a resistor. The resistive component of the input impedance is usually greater than 100 ohms, which is relatively large compared to the 4 to 8 ohms that is the typical input impedance of a moving coil, loudspeaker driver. As a consequence, if the piezoceramic driver for a high-frequency loudspeaker is connected directly in parallel with a lower frequency, moving-coil loudspeaker, the high frequency transducer produces a relatively low output at the higher frequencies as compared to the audio signal output of the moving-coil loudspeaker at the lower audio frequencies. The difference in the relative outputs of the two speakers produces an undesired unbalance in the spectrum of audio frequencies produced by the speaker system.
A further undesirable property of the piezoceramic driver is that the capacitive component of the input impedance of the piezoceramic transducer "loads down" the output of the signal generator or amplifier at the higher frequencies where the reactance of the capacitor is relatively low. Also, the capacitor's reactive characteristic may produce sufficient phase angle to the current supplied by the amplifier to cause the amplifier to become unstable.